From what I remember the later ones had a mechanical switch (ball-bearing?) that rolled back and forth.
I had a few NOS Schwinn taillights (as on Phantom, etc) way back and IIRC that's how they worked.
The 1940s-50s Delta (as on Elgin, Higgins, others) and early Phantom used this switch at the hub:
I do remember something about there being a 3rd type of tl for Schwinn, but don't remember if it was a cosmetic difference or a difference in the switching mechanism...may be mercury switch...?